external display only working after re-login (kde5)

A problem has occurred a few weeks ago during an upgrade of my system - that problem also existed about a year ago or so but then went away “by itself”, so I never reported it. But now it has come back.

When I log into my laptop, in its docking station, with an external VGA screen connected, that external screen remains dark after completion of the login - the laptop itself displays what it should be showing on that external display and not what should be on “its own” screen. The only way to get back my normal configuration is by logging out (not rebooting!) and logging in again, with the same user. After that slightly annoying operation, everything appears as it should.

A strange detail is that, when I pick the logout from the task bar (on the laptop screen because as mentioned, the external screen is dark), the confirmation dialog box shows up on the external screen.

No problems occur if I use the laptop alone, with the external screen.

It is a Dell Latitude E6330, and I am running the latest QT5 frameworks etc, regularly applying all minor and major updates.

As was the case with this at the earlier occasion, the problem disappeared with the major update that arrived today, so this thread can be closed or even deleted.